so say u want to rock spacers this summer

[jrkoupe]

at what point might u need longer bolts?


how much thread needs to be in the hub?....

Im thinking like up to 10-12 mm spacer, max

I run studs on a track car.....but I dont want that look an the street coupe.

grazi

[Tim95M3]

You need longer bolts with any size spacer.

[jrkoupe]

y do u say that?...........or do u mean "just to be safe..."

are our oe bolts at like at the min length?



wonder if BMW makes a longer bolt....hmmmmm

[jrkoupe]

longer bolts avail?...yes of course. i didnt want spacers to end up costing all this...siiiigh

http://www.bimmerworld.com/Wheels-Ti...SABEgL-KvD_BwE

[rf900rkw]

12mm bolts need 12mm thread engagement.

[rf900rkw]

eBay for spacers and matching bolts priced less than the boutiques want for stencilling their logo on the same spacers.

[jrkoupe]

Id do ebay spacers.....

bolts?..not so sure....but Ill look

too many horror stories of students on track w/ sheared studs.

[rf900rkw]

That is because threaded in studs are a sin against good engineering. It's not a question of is the stud will break at the root thread, only a question of when. In our application bolts are vastly superior. I will not run threaded in wheel studs on a lawn mower. I have no problems using the bolts supplied with the eBay spacers.

[jrkoupe]

I did not know that inherently threaded in studs were a no no


I assume most -all race /track cars use them?

[rf900rkw]

No auto manufacturer ever had used threaded in wheel studs. No pro racing organization used them either, they modify or make hubs to use proper press in studs. Unfortunately our stock hubs do not have the meat needed to support a pressed stud nor to even under cut the thread root for stress relief.


May I suggest reading all four of Carroll Smith's books. While some of the specifics may be a bit dated, the sections on stress and design apply every bit as much today as when the books were written. If you find those appealing or useful and want more, the experimental aircraft society has a lot of information aimed at the home engineer. Those guys are big on fatigue failure prevention....

[JoshS]

Racing/track cars convert to thread-in studs for two main reasons:

1) It makes it MUCH easier to mount wheels up. And when you do it 5-10 times a weekend, it makes a huge difference.
2) You can vary wheels/spacers without digging those other studs out of the trailer (although admittedly, sometimes you have to dig those other NUTS out of the trailer, so ...)

That doesn't mean that they aren't a suboptimal fastener -- they are. It's just that the benefits outweigh the risks when it makes sense.

[jrkoupe]

rf..I have some of those books.....not saying Ive read them...lol

Josh....I know y racers use studs..., I just never knew they were inherently weak ish

[MartyBtoo]

The issue is screw-in studs, not studs in general. The act of cutting threads on the bottom portion reduces the effective diameter strength-wise, and the flange they screw into provides a perfect pivot to work on if there is enough force to move the studs. Now if you want to drill out the flange threads and press in studs, all of those issues go away.

Marty

[trkshoe]

I prefer studs as well... but if you must stick with screws, my rule of thumb is at least 5 full rotations of engagement.

[deni2s]

I prefer studs as well... but if you must stick with screws, my rule of thumb is at least 5 full rotations of engagement.

If I am not mistaken, there are tests that more than 3 rotations are not improving situation anymore under direct constant force. Vibration might be another factor not taken into consideration on these tests.

[BimmerBreaker]

I run studs and have never had a problem

Yes they may not be the optimal design, but I like how they look, like not worrying about bolts when I swap spacers, I like being able to quickly slap my wheel onto the hub without thinking, and I personally believe that if track cars can go through many track events with studs and not have problems, then I won't have problems in my significantly easier-on-the-car street driving.

[jrkoupe]

I did not want to open a can of worms about safety of screw in studs......

but as a track vet of over 14 yrs, I have heard MANY bad stories related to screw in studs.... and never any re bolts.

that being said I use them on track car and change out every 3 yrs.

[Harvey Mushman]

If I am not mistaken, there are tests that more than 3 rotations are not improving situation anymore under direct constant force.

The whole "only three threads are doing all the work" is a bit of an old machinist's tale, and the number varies.

Thread pitch, bolt diameter, tolerances, materials--that all plays a factor. Some believe that if there are X number of turns on a factory bolt, then there should be at least as many turns on an aftermarket bolt when using a spacer.

However, if you look at how many threads there are in the hubs themselves (5-6 typically), then that tells you the maximum number of threads that are in contact with the bolt at any time. So if you're really looking to save money/weight/whatever, then you could measure how far in the bolt needs to go to maximize contact area within the hub, then measure how far the bolt pokes into the wheel when installed, and buy spacers/bolts accordingly.

Or you could just buy a 10mm longer bolt when using a 10mm thick spacer, and save yourself the effort.

[MartyBtoo]

I'm not a fan of most studs unless you are drilling the hub to use press-in ones, but I will say that the newest APEX wheel studs seem to have done away with most of my concerns by having a flat flange that contacts the face of the hub, thereby taking the load that would be on the threads at the hub interface. Has anyone heard of any problems with them?

Marty

[rf900rkw]

I too did not mean to turn this into a stud thread. But to answer, there are two strategies used to get around the inherent flaw of the screw in stud. One is material selection, the other fancy design to move the shear loads away from the critical root thread. Due to the limited space and hub material, neither strikes me as fully effective.

Marty, do you know of anyone that has fitted press ins? When I talked to engineering at a bolt manufacturer, giving them the dimensions, they thought there wasn't enough hub to properly stabilize the stud.



Back to the subject at hand. Choose your wheels. Do the math to determine your required spacer. Buy the spacers with matching bolts once and be done.

[MartyBtoo]

I don't know of any Z3's with pressed in studs. I did put some in my 47 Plymouth, but the axle flanges were about 3 times the thickness of the Z3's.

Marty

[jrkoupe]

I too did not mean to turn this into a stud thread. But to answer, there are two strategies used to get around the inherent flaw of the screw in stud. One is material selection, the other fancy design to move the shear loads away from the critical root thread. Due to the limited space and hub material, neither strikes me as fully effective.

Marty, do you know of anyone that has fitted press ins? When I talked to engineering at a bolt manufacturer, giving them the dimensions, they thought there wasn't enough hub to properly stabilize the stud.



Back to the subject at hand. Choose your wheels. Do the math to determine your required spacer. Buy the spacers with matching bolts once and be done.

lol.....

I just want to have a more flush look, esp in rear....I run e 36 m3 ltw forged wheel.......7.5/8.5.....I want the rears to fill up more wheel well...thats all.